SCANNING SET TRANSISTOR MICROSCOPE

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We studied the effect of energy dissipation on macroscopic quantum tunneling (MQT) in single small Josephson junction. We succeeded in observing dissipative phase transition. Energy dissipation was tuned by attaching a resistor at the very vicinity of small Josephson junction. Here we kept the normal state tunneling resistance of Josephson larger than the quantum resistance, and varied the resistance of the attached resistor. In case of Ohmic shunt resistor made of nickel chromium alloy, the Josephson junction that exhibits insulating behavor recovers superconductivity when the shunt resistance Rs was less than the quantum resistance Rq=h/4e2. On the other hand, when Rs > Rq, it was insulating. We determined the phase diagram for superconductor-insulator transition by varying EJ/EC values. The case of tunneling resistance was also studied. A normal small tunneling junction was connected to a small Josephson junction in parallel. The ohmic shunt resistor and the tunneling junction have different types of energy dissipation in that the charge transfer in the former case is continuous while in the latter discrete. In a theoretical prediction, the phase diagrams for the S-I transition are different between these two. In preliminary experiments, the tunneling junction acted quite similarly to the ohmic shunt resistance.